The present application relates to the hyperacuity printing arts. It finds particular application in conjunction with text rendering and lineart drawing or line stroking and will be described with particular reference thereto. It is to be appreciated, however, that this technique will also find application in other areas.
In bit map rendering and drawing techniques, an image is divided up into a rectangular grid of very small cells, each of which may be black or white. Because each cell may be only black or white, the picture can then be stored as a series of bits, one bit for each cell, i.e., a bit map of the image.
One difficulty with bit map images resides in the stair-stepping artifact that occurs when producing straight edges that are not perfectly aligned with the vertical or horizontal structure of the bit map. The stair-stepping artifact is most pronounced when the edge to be rendered is almost horizontal or vertical. In such straight lines, the edge passes along a line of pixels for a distance which is dependent upon the degree of offset from horizontal or vertical, then steps to a next adjoining line of pixels for some distance, then steps again to the next adjacent line, etc. This stair-stepping seriously degrades the visual quality of the resultant image.
To suppress the stair-stepping, drawing generation programs, such as page decomposition language (PDL) programs, typically increase the resolution, i.e, more bits per line and more lines per inch. This, of course, does not remove the stair-stepping, but merely make finer or smaller steps such that it is harder for the human eye to detect the steps. Resolution, however, is expensive in that halving the bit size doubles the number of bits per line and doubles the number of lines per inch, i.e., requires four times as much information, hence, four times as much processing time and much more precise scanning and printing equipment.
A hyperacuity printer improves the image quality by eliminating or reducing stair-stepping, without increasing overall resolution. In hyperacuity printing, information concerning the location where the edges are to be printed is maintained with a high degree of accuracy, but without increasing the resolution of the input data. Instead of using a bit map of the desired image of text (or lineart) to be printed, a bytemap is used. Each bit position is replaced with a multi-bit byte of coded information, such as a gray value or pixel. The information contained in these multi-bit gray pixels is processed with neighboring gray pixels within the hyperacuity printer to generate an identification of where the edges should be placed. This information, in turn, is used to adjust the exposure in the printer in an optimal manner in order to produces edges that do not have stair-stepping, but remain straight. Typical exposure parameters include intensity which adjusts the overall size of the printer dot (typically used for edge adjustments in a direction transverse to the fast scan direction) and timing to shift the position of the dot along the fast scan direction. An appropriate hyperacuity printer is illustrated in U.S. Pat. No. 5,485,289 of the inventor herein.
The present invention contemplates a new and improved technique to convert line information generated by drawing programs, such as PDL programs and others, into appropriate format for display on a hyperacuity printer.